During the 19th century, ______

During the 19th century, ______ was a most important reason for a century-long population decline in Ireland.
A、war
B、flood
C、famine
D、earthquake
【正确答案】：C
【题目解析】：19世纪的饥荒是导致爱尔兰长达一个世纪人口下降的最重要原因。